AlCl3
Aluminium Chloride

Aluminium chloride is an inorganic chemical compound; it is the chloride of aluminium with the molecular formula AlCl3.

Chemical properties

The anhydrous aluminium chloride in particular likes to attract water and dissolve in the process; it is highly hygroscopic. It smokes in the air and decomposes to form hydrogen chloride. Due to contamination with ferric chloride, the colourless crystals are often light yellow. They react very violently when heated strongly with water to form hexahydrate. This is more stable. It dissolves in water and forms an acidic solution. After a while the aqueous solution becomes turbid due to precipitation of aluminium hydroxide. By adding diluted hydrochloric acid a clear solution is obtained again. No anhydrous aluminium chloride can be obtained from the hexahydrate by heating. Therefore, no aluminium chloride remains after evaporation of the solution, aluminium metahydroxide and hydrogen chloride are formed:

AlCl3 - 6 H2O → AlO(OH) + 3 HCl + 4 H2O

Production

In industry, anhydrous aluminium chloride is produced by the reaction of aluminium with chlorine or hydrogen chloride.

2 Al + 3 Cl2 → 2 AlCl3

Use

Aluminium chloride is a strong Lewis acid and is a compound of numerous additions. It is therefore suitable as a catalyst in the chemical industry. These are needed, for example, in Friedel-Crafts syntheses, in polymerisations or in catalytic cracking.

Like aluminium sulphate, aluminium chloride also serves as a flocculant for drinking water treatment.

Hexahydrate has a haemostatic and disinfectant effect, so it was used as an astringent in deodorants or in antiseptic products. Against light inflammations in the throat, solutions containing aluminium chloride or aluminium chlorate are offered for gargling. It is freely available in pharmacies and drugstores.

Aluminium chloride is used in thin layer chromatography in the form of a spray reagent for the detection of flavonoids. For this purpose, 2.0 g aluminium chloride hexahydrate is dissolved in 100 mL of a 5 % solution (V/V) of glacial acetic acid in methanol. After spraying this solution onto the DC plate, the observation is carried out in UV365 light. This reagent is listed under the designation Aluminium Chloride Reagent R in the European Pharmacopoeia (Ph. Eur.).

Security

In 2014, aluminium chloride was included by the EU in the Community rolling action plan (CoRAP) under Regulation (EC) No 1907/2006 (REACH) as part of the substance evaluation. This involves reassessing the effects of the substance on human health and the environment and, if necessary, taking follow-up action. The reasons for the inclusion of aluminium chloride were the concerns about worker exposure, high (aggregated) tonnage and risk characterisation ratio (RCR) and the risks associated with possible classification in the CMR group.

The reassessment has been underway since 2015 and is carried out by France. In order to be able to arrive at a final assessment, further information was requested.